Conversion of hydrocarbon oil



April 4, 1939. R. J. DEARBORN CONVERSION OF HYDROCARBON OIL Filed Aug. e, 1936 filare ATTOR N EY Patented Apr. 4, 1939 PATENT OFFICE CONVERSION OF HYDROC'ARBON OIL Richard J. Dearborn, Summit, N. J., assignor to The T'exas Company, New York, N. Y., a corporation of' Delaware Application August 6, 1936, Serial No. 94,544

1 Claim.

This invention relates to the conversion of high boiling hydrocarbons into lower boiling hydrocarbons suitable for motor fuel and pertains more particularly to the processing of relatively 5 heavy oils not amenable to the high temperature drastic cracking treatment essential to produce maximum yields o1 high .anti-knock gasoline, due to their tendency to form coke.

One factor limiting the cracking treatment of the heavy oils, such as crude, reduced crude, heavy gas oil, and other oil stocks containing constituents dii'licult to vaporize is the rapidy formationrof coke, which fouls the heating tubes and other parts of the cracking equipment. For each particular heavy oil cracked under conventional methods there is a more or less fixed relationship between the amount of coke formed and gasoline produced at various degrees of cracking. In view of this relationship, the cracking temperature and the length of time at which the oil is subjected to cracking treatment is limited to avoid the formation of troublesome coke deposition at the sacrifice of gasoline yield in this initial cracking stage in order to extend the length of operating runs.

In accordance with present practice these heavy oil stocks are subjected to a relatively mild cracking treatment, commonly known as viscosity breaking, regulated tol produce an optimum yield of intermediate clean condensate. The cracked products are then separated into vapors and residue and the vapors fractionated to condense and separate the higher boiling constituents as" intermediate cycle stock from the gasoline produced from the process. The residue re-. sulting from this viscosity breaking treatment, with or Without further treatment tol free it of any lower boiling constituents contained therein, is ordinarily rejected from the process as fuel oil or converted into solid coke by further treatment.

The intermediate cycle stock, formed by the initial mild cracking of the heavy oil, is then subjected to high temperature drastic cracking treat- 5 ment in a second stage to produce an optimum yield of gasoline of high anti-knock characteristics. The character of the intermediate cycle stock permits the production of a much larger yield of high anti-knock gasoline with a lesser amount of carbon deposition than do the original crude stocks or other stocks containing constituents diiiicult to vaporize.

` Another facto-r, in addition to the formation of coke, limiting the extent oi cracking in the second stage is the formation of gaseous constituents boiling below the range of gasoline. While these gases do not interfere with the operation of the process, they do limit the yield of gasoline produced, and in many cases the extent of cracking of the intermediate gas oilin the second stage is limited to avoid excessive gas losses rather' than to avoid coke diiiiculties.

My invention has for its principal object the improvement o the process of the general nature above outlined so as to produce a better yield of high anti-knock ygasoline with a lesser amount of processing and equipment.

In accordance with my invention the intermediate cycle stock resulting from the viscositybreaking treatment, after undergoing high temperature cracking treatment, in the second stage for a maximum period, limited to avoid troublesome coke deposits, is merged with the residue from the viscosity-breaking treatment and the combined products thereafter subjected to further cracking treatment after which the products are separated from vapors and residue and the vapors fractionated in a conventional manner.

According to another phase of my inventionl a light intermediate cycle stock formed by iractionating the vapors from the second stage is subjected to further independent cracking treatment in a third stage and the products from the third stage treatment introduced into the Zone in which the vapors from the viscosity-breaking treatment are fractionated so that the higher boiling constituents from the third stage treatment are passed to the second stage for further treatment therein.

When carrying out the process in accordance with the principles of my invention, as briey outlined above, the ultimate gas loss from the process may be substantially below what would normally be expected from the extent of cracking to which the charging stock has been subjected and the total yield of gasoline is greater than may be expected from the extent of cracking. In other words, the ratio of gasoline produced to the amount of gas formed is greater than may be expected from the character of the treatment given.

While the cause oi these results has not been definitely established, there are a number of possible explanations. First, the heavy residual constituents introduced into the products undergoing high temperature vapor phase cracking in the second stage after these products have undergone extensive cracking may serve as a solvent for asphaltenes and carboids which begin to form as the cracking proceeds and prevent deposition of these materials on the Walls of the heating tubes, thus permitting a greater amount of cracking of the clean condensate stock in the second stage.

Second, the heavy residual constituents introduced into the products undergoing high temperature vapor phase cracking after these products have undergone extensive cracking soas to form a relatively high concentration of gaseous constituents may reactwit'h such gases to form hydrocarbons in the gasoline boiling range, or these heavy residual constituents may tend to promote the polymerizationor alkylation of such gases into higher boiling compounds within the gasoline boiling range.

Third, the cracked products undergoing conversion in the second stage, upon contacting with the residue from the viscosity-breaking treatment, may serve as a carrier or diluent for the residual constituents and'permit more extensive cracking of the residue.

Whatever the underlying causes may be, very definite advantages may be realized by processing the oil in accordance with my invention.

Other more specic objects of my invention will beapparentfrom the more detailed description hereinafter in which reference is made to the accompanying drawing diagrammatically illustrating an .apparatus suitable for carrying out myinvention.

Referring now vtothe drawing, the reference numeral I Il designates a charging line through which fresh charging oil is introduced into the system. This fresh charging oil is preferably a crude stock, such as crude, topped or reduced crude, .butmay be a heavy gas oil. The fresh charging stock passing through line I is forced bymeans of pump II located therein to a heating coil I2 located in the furnace I3 wherein a fresh charging oil is heated to a crackingftemperature after which it discharges through transfer line I4.into a separating chamber I5.

The temperature and time of treatment of the oil Vduring its passage through the coil I2 .will depend upon the character of the oil charged thereto. When operating on reduced crude the oilmay be heated to a temperatureof from 800 to 900 F., for example, and maintained at cracking temperature for a period sufficient to convert 3,0% thereof into constituents boiling below the boiling range Yof the charging oil of whichfrom 8 to 15% may be within the gasoline boiling range.

The products, Yafter being introduced into the separating chamber I5, separate into vapors and residue, the vapors passing overhead through line I6 to a fractionating tower I1. The upper end of the separating chamber I may be provided with baffles to knock down entrained liquid prior to the passageof the vapors into the fractionating tower I1, and a reflux oil may be introduced into the top of the chamber.

Vapo-reintroduced into the fractionating tower I1 are subjected to fractionation to separately condense insufliciently cracked constituents as reflux condensate. The fractionating tower is provided with suitable gas liquid `contact elements, such as bubble trays, to effect rectification V,of the vapors passing therethrough. The upper end of the fractionating tower I1 is provided with suitable cooling means such as trimming coil I8 to regulate the top temperature so as to condense insufficiently cracked constituents within the fractionating tower I1. Suiciently cracked constituents remain uncondensed in the tower I1 and pass overhead through line I9 to a condenser 2|, wherein the sufficiently cracked vapors within the gasoline boiling range are condensed. Products fromV the condenser 2l pass through line 22 to a receiving drum 23v wherein fixed gases separate from the desired distillate. The fixed'gases pass overhead through line 24 provided with a valve 25 for regulating the back pressure on the system and maybe passed to a suitable gas lrecovery plant not shown. The desired distillateseparated in the receiving drum I1 is withdrawn therefrom through line 21 provided with pump 28 and is forced through heat- .ing coil 29 located in the furnace I3 wherein the oil is subjected to high-temperature, vaporphase cracking conditions. The oil, after being heated to the desired cracking temperature in coil 29, continues through a soaking coil 33, located in the convection section of the furnace, where it is maintained at high cracking temperature until cracking has proceeded to a point just short of that at which asphaltenes and carboids begin to precipitate on the walls of the heating tubes. These cracked products are then merged with residue separated from the cracked products from the heating coil I2 in the separating chamber I5. To this end the residue is Withdrawn from the bottom of the chamber I5 through line 3| provided with pump 32 and is injected into the stream of cracked products undergoing final conversion in the soaking coil 33.

The mixture of residue and cracked products from coil 29 is subjected to further conversion conditions in the final section of the tubular soaking coil 33, after which it discharges through line 34 to a separating chamber 35 wherein vapors separate from residue.

The residue from the separator I5 may pass through lines 3| and 65 to the outlet of the heating coil 29 and then merge with the vapor phase products undergoing cracking, or a portion orall of the residue may pass through lines 3| and 55 and merge with the vapor phase products at one or morepoints in the iinal section of the soaking coil 33.

'I'he upper section of the chamber 35 may be pro-vided with baffles for the purpose of removing entrained liquid before passing overhead through line 36 to the bottom section of a fractionating tower 38. The fractionating tower 38 is provided with suitable fractionating elements, such as bubble trays, for effecting vapor-liquid contact, and the top temperature is regulated by a trimming coil 39 or by direct reuxing to condense insufficiently cracked constituents.

sufficiently crackedconstituents, together with fixed gases, pass overhead through line 40 to a condenser 4I wherein the sufficiently cracked constituents within the boiling range of gasoline condense as a final distillate. Products from the condenser 4I pass through line V42 to a receiving drum 43 wherein the desired distillate separates from the fixed gases. The fixed gases pass overhead through line 44 provided with a valve 45'for regulating the back pressure on the system and may pass to a suitable gas recovery plant not shown. The desired distillate is Withdrawn from the receiving drum 43 through line 46 and, if desired, a portion thereof may be returned tothe upper end of the fractionating-tower 38 to serve as a reflux therein. Unvaporized residue separated in -the separating chamber 35 is withdrawn from the bottom thereof through line 41 from whence it may pass to a storage tank, not shown, or may be subjected to further treatment in a conventional manner.

In accordance with one phase of my invention the total refluxcondensate formed in the fractionating tower 38 is withdrawn from the bottom through line I8` as a final distillate fuel oil. According-,to another phase of my invention a portion or all of this condensate may be subjected to further cracking treatment, as hereinafter described.

When operating in accordance with the latter method the fractionating tower 38 may be provided with a trap-out tray 49 from whence condensate collected therein may be withdrawn through line 50 and forced by means of pump I located therein through a separate heating coil 52 located in the furnace 53. The oil, during its passage through the coil 52, is subjected to high temperature cracking conditions after which it emerges through line 54 and may pass through line 55, forming an extension thereof, into the bottom section of the fractionating tower Il wherein it commingles with the vapors introduced therein through line I6, or, if desired, a portion or all of the cracked products passing through line 54 may be passed through line 56 and introduced into the separating chamber I5 into which the cracked products from the heating coil I2 discharge.

The pressure maintained in the various parts of the equipment above referred'to may be substantially uniform throughout, except for the necessary difference to effect the desired flow, or a differential pressure may be maintained between the heating coils I2, 29 and 52 and the separating chambers I5 and 35, in which case the transfer lines I4, 34 and 54 are provided with suitable reducing valves 51, 58 and 50, respectively, to produce the desired reduction in pressure. In practice, it is preferred to maintain the heating coil I2 and separating chamber I5 under a pressure somewhat below that maintained in the heating coils 29, 52 and separating chamber 35. For example, the oil passing through the heating coil I2 may be maintained under an outlet pressure of from 200 to 400 pounds per square inch, whereas the oil passing through the heating coils 29, 33 and 52 may be maintained under a pressure ranging from 400 to 1000 pounds per square inch, for example.

The following example will serve as a guide in carrying out my invention to obtain the greatest benefit therefrom, it being understood that the values given in the example are illustrative rather than limitative.

Mid-Continent reduced crude having an A. P. I. gravity ranging from 20 to 26 is passed through the heating coil I2 regulated to heat the oil to a temperature ranging from 800 to 900 F., preferably between 850 to 875. The oil is maintained at this temperature for a period suicient to convert from 15 to 30% thereof into constituents boiling below the boiling range of the original charge, of which from 8 to 15% thereof may be within the gasoline boiling range. The heating coil I2 is maintained at an outlet pressure ranging from 50 to 400 pounds per square inch. The separating chamber I5 is maintained under a somewhat lower pressure, such as from 25 to 100 pounds per square inch. The fractionating tower I1 is regulated to take overhead a fraction having an end point corresponding to that of the desired motor fuel or, if desired, a portion of the heavy naphtha may be condensed within the fractionating tower I1.

Condensate from the fractionating tower I'I, upon passing through the heating coil 29 and soaking section 33 thereof, is heated to a temperature ranging from 900 to 1050 F. or thereabouts. The oil is maintained at this temperature in the soaking section 33 for a period adequate to convert from about 20% to 40% thereof into gasoline constituents before merging with the residue from the bottom of the chamber I5. The merged products, during passage through the remainder of the soaking coil 33, are maintained at a temperature of from 850 to 925 F. and preferably between 900 and 925 F. The outlet pressure of the soaking coil 33 preferably ranges from 200 to 600 pounds per square inch.

The top temperature of the fractionating tower 38 associated with the separating chamber 35 is regulated to take overhead the desired distillate products which may have an end point of from. 400 to 437 F.

In event condensate from the fractionating tower 38 is subjected to further cracking, this oil, during its passage through the heating coil 52, may be heated to a temperature ranging from 900 to 1050 F. and maintained at a coil outlet pressure of from 200 to 600 pounds per square inch.

Having described the preferred embodiment of my invention, it will be understood that it embraces such other modifications and variations as come within the spirit and scope thereof and that it is not my invention to unnecessarily limit the invention except as necessary to distinguish from prior art.

I claim:

A method of treating hydrocarbon oil to form lower boiling hydrocarbons suitable for motor fuel which comprises passing charging stock comprising the residual constituents of crude petroleum once through a single-pass cracking zone wherein it is subjected to cracking conditions of temperature and pressure to effect conversion into lighter products, directing the resultant cracked products into a primary separating zone wherein separation of vapors from liquid residue occurs, subjecting the separated vapors to fractionation in a primary fractionating zone to separate a reiiux condensate from lighter products, passing said reux condensate through a primary section of a cracking coil under superatmospheric pressure and applying heat thereto to subject the oil flowing therein to cracking temperature and effect conversion into lighter products, withdrawing liquid residue from said primary separating Zone and merging said liquid residue with the products from the primary section of' said cracking coil for passage through a subsequent section thereof while applying heat thereto to maintain the merged products at cracking temperature and effect conversion into lighter products, passing the resultant cracked products from said cracking coil into a second separating zone wherein separation of vapors from residue occurs, passing the separated vapors into a second fractionating zone wherein the vapors are fractionated to separate a reflux condensate from lighter products, subjecting the later reflux condensate to cracking conditions of temperature and pressure in` a separate cracking zone to effect an additional conversion into lighter products and directing the resultant cracked products into the primary separating zone.

RICHARD J. DEARBORN. 

